FIG. 15 is a sectional view of a conventional loudspeaker diaphragm 47 made of resin. Diaphragm 47 is formed by thermally melting resin pellets and injection-molding them with a die. The resin pellets are made of single resin material, such as polypropylene. Furthermore, the resin pellets may be made of different resin to adjust physical properties of the diaphragm, that is, properties of a loudspeaker or a sound quality. If a physical property which can hardly be adjusted with such resin, the property may be adjusted by mixing reinforcing material, such as mica, in the resin pellets, so that properties of the loudspeaker and a sound quality may be adjusted.
Resin of conventional diaphragm 47 mainly contains polypropylene. Polypropylene is material derived from petroleum, and therefore, generates an additional amount of carbon dioxide when it is incinerated and wasted, thus affecting environment.
In order to reduce the affect to environment, the use of polylactic acid that is resin derived from plant has been developed. Patent Document 1 discloses a conventional diaphragm made of polylactic acid.
The conventional diaphragm made of polylactic acid does not have high reliability due to insufficient resistance to heat, and has insufficient strength and low elasticity, having a problem in sound quality.    Patent Document 1: JP2005-260546A